High Solubility of Hetero-Valence Ion （Cu^2＋） for Reducing Phase Transition and Thermal Expansion of ZrV1.6P0.4O7

Large thermal expansion at room temperature and high phase transition temperature of ZrV2O7 limit its practical applications and are reduced by the high solubility of hetero-valence ion （Cu^2＋） on the basis of an equal-valence substitution of P^5＋ for V^5＋. The temperature-dependent Raman spectra show that Zr0.9CU0.1V1.6P0.4O6.9 maintains a normal parent cubic structure till 173 K and transforms to a 3 × 3 × 3 cubic superstructure below 173K. Temperature dependent x-ray diffraction patterns of Zr0.9CU0.1V1.6P0.4O6.9 show near zero and negative thermal expansion. High solubility of lower valence Cu^2＋ relates to an equal-valence substitution of smaller pH for P^5＋, which extends the bond angle of V（P）-O-V in ZrV1.6P0.4O7 close to 180°. The change of microstructure is considered to be responsible for reduced phase transition temperature and thermal expansion.     

Phase transition and thermal expansion property of Cr_(2-x)Zr_(0.5x)Mg_(0.5x)Mo_3O_(12) solid solution

Compounds with the formula Cr2-xZr0.5xMg0.5xMo3O12（x = 0.0, 0.3, 0.5, 0.9, 1.3, 1.5, 1.7, 1.9） are synthesized, and the effects of Zr4＋ and Mg2＋ co-incorporation on the phase transition, thermal expansion, and Raman mode are investigated. It is found that Cr2-xZr0.5xMg0.5xMo3O12 crystallize into monoclinic structures for x 〈 1.3 and orthorhombic structures for x _〉 1.5 at room temperature. The phase transition temperature from a monoclinic to an orthorhombic structure of Cr2Mo3O12 can be reduced by the partial substitution of （ZrMg）6＋ for Cr3＋. The overall linear thermal expansion coefficient decreases with the increase of the （ZrMg）6＋ content in an orthorhombic structure sample. The co-incorporation of Zr4＋ and Mg2＋ in the lattice results in the occurrence of new Raman modes and the hardening of the symmetric vibrational modes, which are attributed to the MoO4 tetrahedra sharing comers with ZrO6/MgO6 octahedra and to the strengthening of Mo-O bonds due to less electronegativities of Zr4＋ and Mg2＋ than Cr3＋, respectively.     

Near-zero thermal expansion of In_(2(1-x))(HfMg)_xMo_3O_(12) with tailored phase transition

Solid solutions of In_(2(1-x)(HfMg)_xMo_3O_(12) are synthesized by solid state reaction with the aim to reduce the phase transition temperature of In_2Mo_3O_(12) and improve its thermal expansion property.The effects of(HfMg)~(6+) incorporation on the phase transition and thermal expansion are investigated.It is shown that the monoclinic-to-orthorhombic phase transition temperature obviously decreases and the coefficient of thermal expansion(CTE) of the orthorhombic becomes less negative and approaches to zero with increasing the content of(HfMg)~(6+).A near zero thermal expansion covering the case at room temperature(RT) is achieved for the solid solutions with x ≥ 0.85,implying potential applications of this material in many fields.     

Er3+掺杂NaAl(MoO4)2的荧光光谱与上转换发光研究

用液相沉淀法制备得到掺稀土离子Er3+和Ce3+的NaAl( MoO4)2,X射线衍射图样显示NaAl(MoO4)2是单斜晶体结构.掺稀土离子Er3+和Ce3+的NaAl(MoO4)2的拉曼光谱研究表明,掺Er3+离子的NaAl(MoO,)2比掺Ce3+离子具有更强荧光性能,掺杂Er3+离子的NaAl( MoO4)2晶...     

Al~(3+)/Mo~(6+)双离子取代ZrV_2O_7中Zr~(4+)/V~(5+)实现近零膨胀

采用固相烧结法制备了Zri_(1-x)Al_(2-x)V_(2-x)Mo_xO_7(0≤x≤0.9),并通过调整Al~(3+)/Mo~(6+)对ZrV_2O_7中的Zr~(4+)/V~(5+)离子替代量来实现近零膨胀,对于较小的x值(x≤0.3),材料保持了与ZrV_2O_7相同的立方相结构.随着Al~(3+)/Mo~(6+)替代量的增加,(Al/Zr)~-和(Mo/V)~+之间的库仑相互作用逐渐加强,这种库仑相互作用导致材料中未发生畸变的立方相晶体结构逐渐减少.当x≥0.7时,材料中立方相晶体结构完全消失.在425-750 K温度区间内,Zr_(0.5)Al_(0.5)M_(0.6)O_7展示出近零膨胀性质(-0.39×l0~(-6)K~(-1)).Zr_(0.5)Al_(1.5)V_(1.5)Mo_(0.5)O_7的低热膨胀性能可能与Al~(3+)/Mo~(6+)对ZrV_2O_7中Zr~(4+)/V~(5+)部分替代引起部分晶体结构发生的畸变及其对未替代部分的晶格结构的影响有关.     

Zero and controllable thermal expansion in HfMgMo_(3-x)W_xO_(12)

HfMgMo_(3-x)W_xO_(12) with x = 0.5, 1.0, 1.5, 2.0, and 2.5 are developed with a simple solid state method. With increasing the content of W, solid solutions of Hf Mg Mo3-xWx O12 crystallize in an orthorhombic structure for x≤2.0 and a monoclinic structure for x2.0. A near-zero thermal expansion(ZTE) is realized for HfMgMo_(2.5)W_(0.5)O_(12) and negative coefficients of thermal expansion(NCTE) are achieved for other compositions with different values. The ZTE and variation of NCTE are attributed to the difference in electronegativity between W and Mo and incorporation of a different amount of W, which cause variable distortion of the octahedra and softening of the MoO_4 tetrahedra, and hence an enhanced NCTE in the a- and c-axis and reduced CTE in the b-axis as revealed by Raman spectroscopy and x-ray diffraction.     

Y_(2-x)(LiMg)_xMo_3O_(12)固溶体吸水性与热膨胀性能研究

Y2-x(LiMg)xMo3O12固溶体(x=0、0.1、0.3、0.5、0.7、0.9、1.1、1.3、1.5、1.7、1.9和2.0)采用固相法制备。当x=0时,由于严重吸水,拉曼峰宽化。随着(LiMg)掺入量的增加,拉曼峰趋于尖锐并发生劈裂,说明固溶体的吸水性得到明显的降低,结晶性能提高,变温拉曼光谱显示失水对应的温度也在降低。在900cm-1和370cm-1附近出现的新峰,与Li-O和Mg-O的振动有关。随着(LiMg)量的增加,Li-O和Mg-O的振动加强,并导致MoO4与YO6振动减弱,也可能与热膨胀系数的变化有关。     

γ-Bi2Sn2O7的水热合成及其可见光区光电响应研究

本文采用水热法制备了γ-Bi2Sn2O7并研究了其在可见光区的光电响应.Bi2Sn2O7的晶体结构和光电响应特性分别用X射线衍射和表面光电压谱进行表征.研究结果表明,合成的Bi2Sn2O7呈现γ相立方结构,通过吸收光谱估算光学带隙为2.67eV,比α-Bi2O3(2.85eV)的光学带隙小.Bi2Sn2O7的光电响应相对于α-Bi2O3在可见光区展现出一定的优势,同时对外加电压有很强的响应.     

固溶体Fe_(2-x)Yb_xMo_3O_(12)的相变、吸水性及热膨胀性能

采用固相烧结法,以Yb2O3、MoO3、Fe3O4为原料制备了Fe2-x Ybx Mo3O12(x=0,0.2,0.4,0.6,0.8,1,1.2,1.4,1.6,1.8,2)系列固溶体,并通过X射线衍射图样、Raman光谱、热分析以及膨胀系数测试对其结构、相变、吸水性及热膨胀性能进行了研究。结果表明Fe2-x Ybx Mo3O12当x≤0.4时是单斜相,当x≥0.6时是正交相,随着x值的增加Fe2-x Ybx Mo3O12材料的相变温度逐渐降低。Fe2-x Ybx Mo3O12含有的水分子可以分为两类,一类吸附在晶体表面对晶格振动没有影响,第二类进入晶体内部对晶格振动产生较大影响,导致负膨胀性质的消失,只有完全失去水分子后才表现负热膨胀性能。     

Bias polarity-dependent unipolar switching behavior in NiO/SrTiO_3 stacked layer

The identification of the switching location has been a key technology to tune the physical properties of unipolar resistive switching(RS) cells.Here we report the RS properties of Au/Ni O/Sr Ti O3(STO)/Pt memory cells.The switching repeatability is closely related to the applied bias polarity,which is different from the scenario of the Au/STO/Pt cells reported in our previous researches.The high resistance in positive bias is greater than that in negative bias.The R(T)–R0 I2 R(T) plot of the on-state I–V curve shows a regular shape only with a slight bend and an abnormal shape with an abrupt increase and decrease under negative and positive bias,respectively.These comparative experimental results reveal that the conductance filament consisting of oxygen vacancies grows from the cathode to the anode.The spatial RS location is identified with the weaker part along the conductance filament length direction,which should be near the Ni O/STO interface and STO/Pt interface under positive and negative bias,respectively.